7m842 Freeform Design
Thomas Krijnen 0590144
Introduction
This report has been made on account of the course Freeform Design held at the Eindhoven Technical University in 2010.
In the first part, three polygonal freeform models are provided. Each of them is modelled in the open source modelling package Blender by using different modelling techniques.
In the second part, one of these three design variants is chosen to be remodelled using NURBS in Rhinoceros. NURBS surfaces have several advantages over polygonal models, for instance that they provide an accurate definition of truly curved surfaces instead of a flat polygonal approximation.
The third parts comprises an investigation of the logic behind the design from the first assignments and rebuild it by using Grasshopper, a plug-in for Rhinoceros that provides visual programming in order to conceive generative design models.
The reader is wished a pleasant time reading this report.
Thomas Krijnen
Assignment 1: Three polygonal models
The Metasurface • The Cloth Simulation • The Subdivision Surface
Metasurfaces
Metasurfaces are a great way to help structure interior spaces and their relations. However, the disability to create creases make the use of it to design a outer facade somewhat limited. It is hard to articulate any kind of accents and the uniform blobby appearance makes it hard for the designer to make the building interact with the environment
By making use of metasurfaces to only shape the inner surface and use regular planar techniques for the outer surface, one yield the best of both worlds. Furthermore, it adds a moment of surprise to the entrance because the outer facade does not fully reveal the inner workings of the building.
The following pages outline the procedure of creating such a mesh in Blender, without the use of boolean operations to retain control over triangulation.
fig1
Starting with the mesh representation of the metasurface as it results from the conglomerate of metaballs (fig1), a ground plane is added (fig2).
Because of the way the metasurface is evaluated the mesh consists of planar edgeloops in all three dimensions forming a three-dimensional array of cubes.
fig2
fig3
This enables for the mesh to be easily cut with two horizontal planes (fig3), by deleting the faces that consists solely of vertices above or below a certain z-value.
Secondly, a hole is cut in the mesh that will later form the entrance (fig4), the entrance also aligns with the edgeloops from the metasurface evaluation algorithm.
fig4
fig5
The pattern of edges (fig5) worked out well for cutting the mesh, but some of its irregularities result in smoothing artefacts when gourad shading is applied. To overcome this shading issue, the edges in the model are smoothed (NB an actual smoothing of the geometry is meant here, not just the normals). This alters the shape of the mesh, to ensure that the boundary
fig6
fig7
edges (fig6) remain planar they are excluded from the smoothing step. This is done by locking the vertices that form the non-manifold, i.e. boundary, edges. Note that the smoothing procedure is similar to applying a Relax modifier in 3ds Max.
Now with this a smoother version of the model (fig7), work is needed on the outer
fig8
fig9
side of the model. An outer mesh is drawn with simple planar faces (fig8). The connection with the entrance is made by extruding the edges of the metasurface. To model the thickness of the roof also the top boundary edges are extruded. Blender’s autofill functionality is used to fill in the faces connecting the boundary edges of the roof (fig9).
fig10
For demonstration purposes a low resolution base mesh has been used. The last image (fig10) shows the resulting higher resolution model, including a load bearing structure consisting of a simple grid of beams.
Organisation
To maximize the contrast between the exterior and interior shapes, the floor plan consists of one large open space. Due to the way it is conceived, using metaballs, it clearly provides several zones to which the distinct functions are assigned.
Adjacent to the entrance is a small space in which an information desk, cloakroom and restroom can be situated. Right below that is the zone situated for the permanent exposition. To the left of these are the two zones for facilitating the museum visitors. These provide space for the restaurant, with a kitchen and room for a buffet, as well as a library, an auditorium and a museum gift shop. To the right of the entrance is the temporary exposition situated. This is the only zone without direct daylight. This means that it can be used for all sorts of temporary audiovisual installations as well as static art works that need to be lit carefully. Adjacent to the temporary exposition is the workshop. This is meant to function as an Artist-in-Residence location in which it is possible for artists to conceive their works and exhibit them in the temporary exposition zone.
Appearance
The pattern of shadows, projected by the roof structure on the walls, articulate the curved surfaces of the structure. The granularity of the surface texture is a major means for the human eye for depth perception. The same holds true for the floor where the perspective of the tiles gives an indication of distance and field of view. Lastly, depth perception is increased by the natural colour perspective that manifests itself by the distinction in yellow light from the sun and blue light from the sky interacting with the different surfaces.
Cloth simulations
A lot of freeform designs are inspired by natural phenomena. Gaudi was among the first to experiment with draping cloths and freezing them afterwards to let them maintain their shapes. A great benefit of this working with this method is that the surfaces that originate from such a procedure are close to optimal in relation to their internal forces. With the advent of computer modelling and simulation techniques, experimenting with cloth surfaces has become much easier, several modelling packages provide a cloth simulation ready to be used in modelling work. One of these modelling packages is Blender. The following page will outline a procedure to use a cloth simulation for a roof surface.
fig1
Starting with an evenly spaced grid placed three meter above the ground (fig1), distortions are applied to the grid (fig2). These distortions are the result of selecting a single vertex somewhere in the grid and rotating its neighbouring vertices around that selected vertex with Blender’s proportional editing (similar to 3ds Max’s
fig2
fig3
Soft Selection).
This non-topology altering operation maintains
the edgeloops of the existing grid and thus
makes it easy to select the faces between
two neighbour edgeloops. These faces are
extruded downwards onto the ground plane
and represent the walls of the structure (fig3).
fig4
fig5
The building roof is then evaluated in a cloth simulation, with the wall vertices pinned to provide supports for the cloth. The cloth simulation uses parameters that resemble real world properties, only the gravitational force is reversed, thus creating a surface bulging upwards instead of downwards (fig4). The roof structure that is the outcome of this simulation closely resembles what would be an optimal structure for this roof, i.e. with the minimal internal bending moments in the roof shell and only loaded with pressure forces.
As a last step thickness is applied to the roof structure as well by slightly offsetting the existing surface and connecting it to the wall (fig5).
Appearance
The building has a very strong orientation in its longitudinal direction. This stimulates the circulation of the visitors and ensures they get a view of all that is expositioned. The spaces in the bottom right are the more private, facilitary spaces whereas the other spaces serve as exposition space, library, gift shop and catering.
Organisation
The roof surface looks very organic, as are the walls in the floor plan, in which space flows along the curved walls. But because of the way these walls are extruded and served as a fixation for the cloth, the walls have a very distinct 2.5 dimensional nature. This contrasts with the fully three-dimensional nature of the roof surface. By simulating softbodies instead of cloths this clash between 2.5D and 3D surfaces can be further addressed.
Subdivision surface modelling
When prototyping a freeform building, in initial stages, it is often not that necessary to have total control over each and every square centimetre of the building shell. When using computer modelling packages, what often will be the case is that the designer shapes only a cage in which the modelling package will interpolate a freeform surface. Several algorithms exist for this freeform interpolation, almost every one of them works in a iterative way, progressively smoothing the cage to a smooth surface. In Blender Subdivision Surface modelling is provided by applying a modifier. This means that the end user is able to work on the flat polygonal cage, while simultaneously seeing the smoothed end result. The following page outlines the procedure of how the model, of which the floor plan is printed on the left, originates from the flat polygonal cage.
fig1
Starting with a quad mesh that is the result of some basic polygonal modelling (fig1), a Subdivision Surface modifier is applied in Blender (fig2). The algorithm used in Blender is the Catmull-Clark algorithm. Catmull-Clark is an iterative smoothing algorithm in which both extra topology is added (specifically: edges are subdivided and a vertex is placed at the centroid of all existing faces) and existing vertices are moved according a formula to a location closer to neighbouring vertices.
fig2
On the top of the tower one face has been removed to function as a window. After the subdivision step also the border of this opening has been smoothed to a near circle. This smoothed kind of opening is not the only opening that is required in the building, for the entrance and other windows a more orthogonal kind of shape is desired. Therefore, the Subdivision Surface modifier is applied and work on the mesh continues after that. The holes that are cut in the mesh by deleting faces in this subsequent phase do have that orthogonal quality (fig3).
fig3
As a last step the hull created in the previous steps is given thickness (fig4).
fig4
Organization
The space that this model provides is very versatile and suitable for all kinds of expositions. The facilitary functions will be placed on a small additional floor level in such a way it will not interfere with the open character of the overall exposition space.
Appearance
This design provides a space that resembles Gothic cathedrals from the inside due the high ceilings and vertical windows. The exterior of the building has an industrial quality that resembles the architecture of Erich Mendelsohn in, for example, the Einsteinturm.
